Modern electronic equipment such as televisions, telephones, radios and computers are generally constructed of solid state devices. Solid state devices are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, solid state devices are very reliable because they have no moving parts, but are based on the movement of charge carriers.
Solid state devices may be transistors, capacitors, resistors, and other semiconductor devices. Typically, such devices are formed in and on a substrate and are interconnected to form an integrated circuit. The integrated circuit may be a mixed voltage circuit that has core devices which operate at low voltage to accommodate small device size and to minimize power consumption and heat generation, and input/output (I/O) devices which operate at a higher voltage to interface with other higher voltage devices.
For a complementary metal oxide semiconductor (CMOS) mixed voltage circuit, the core devices are typically field effect transistors with a thin gate dielectric and a low threshold voltage while the I/O devices are typically field effect transistors with a thick dielectric and a high threshold voltage. To optimize performance of both core and I/O devices, masking processes in addition to roadmap CMOS design have been used to provide the dual gate dielectric thickness and to separately form source and drain extensions and pockets for the core and I/O devices. Such additional masking processes are expensive and greatly increase the cost of CMOS mixed voltage circuits.
Efforts to reduce the cost of CMOS mixed voltage circuits have concentrated on minimizing masking processes by co-optimizing the formation of source and drain extensions and pockets for the core and I/O devices using a single masking process. Co-optimization approaches, however, typically fail to achieve high performance core devices because the graded or deeper junctions required for I/O device reliability severely degrades the drive current performance of the core devices.